Eu3+/Sm3+-doped Na2BiMg2(VO4)3 from substitution of Ca2+ by Na+ and Bi3+ in Ca2NaMg2(VO4)3: Color-tunable luminescence via efficient energy transfer from (VO4)3- to Eu3+ /Sm3+ ions

In this article, we acquire a novel Na2BiMg2(VO4)(3) phase (abbreviated as NBMVO) via the substitution of Ca2+ by Na+ and Bi3+ ions in Ca2NaMg2(VO4)(3). A series of Eu3+/Sm3+-doped Na2BiMg2(VO4)(3) phosphors were synthesized via a high-temperature solid-state reaction route. XRD patterns for the prepared samples can be assigned to the standard Ca2NaMg2(VO4)(3) phase. For the Na2BiMg2(VO4)(3) host, the emission spectrum shows a wide band from 400 to 800 nm peaking at 535 nm under the optimal 378 nm excitation, which can be deconvoluted into two symmetric bands around 521 and 579 nm corresponding to transitions T-3(2)->(1)A(1) and T-3(1)->(1)A(1) from the (VO4)(3-) group, respectively. Monitored at 535 nm, the excitation spectrum exhibits a broad band with two peaks at 378 nm (26455 cm(-1)) and 324 nm (30864 cm(-1)), which originate from the transitions T-1(2)<-(1)A(1) and T-1(1)<-(1)A(1) of the (VO4)(3-) tetrahedron, respectively. When Eu3+ or Sm3+ is doped into the host, the emission spectra display both the host and the Eu3+ or Sm3+ characteristic emission peaks upon 378 nm excitation, moreover, the excitation spectra monitored at the Eu3+ (607.5 nm) or Sm3+ (650 nm) characteristic peaks contain both the host excitation band as well as the Eu3+ or Sm3+ characteristic excitation peaks. These results demonstrate an efficient energy transfer from the host to the Eu3+ or Sins' ions. Furthermore, the variation of the emission spectra for samples doped with different Eu3+ or Sm3+ contents under 378 nm excitation (witnessed by a color change from yellowish green to orange/light orange upon 365 nm UV lamp excitation) and the corresponding decay times are further used to validate the energy transfer from the (VO4)(3-) group to the doped ions. The energy transfer mechanisms for NBMVO:Eu3+ and NBMVO:Sm3+ are determined to be electric dipole-quadrupole and dipole-dipole interactions, respectively. These results suggest that these materials have potential as candidate phosphors in UV/n-UV w-LED applications.